Method to reduce module inductance

ABSTRACT

A DC bus for use in a power module has a positive DC conductor bus plate parallel with a negative DC conductor bus plate. One or more positive leads are connected to the positive bus and are connectable to a positive terminal of a power source. One or more negative leads are connected to the negative bus and are connectable to a negative terminal of a power source. The DC bus has one or more positive connections fastenable from the positive bus to the high side of a power module. The DC bus also has one or more negative connections fastenable from the negative bus to the low side of the power module. The positive bus and negative bus permit counter-flow of currents, thereby canceling magnetic fields and their associated inductances, and the positive and negative bus are connectable to the center portion of a power module.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application incorporates by reference in its entirety, andis a divisional of the currently co-pending U.S. patent application Ser.No. 11/292,870, having a filing date of 2 Dec. 2005; which is adivisional of the currently U.S. patent application Ser. No. 10/109,555,having a filing date of 27 Mar. 2002, and now issued as U.S. Pat. No.7,012,810 on 14 Mar. 2006; which is a continuation-in-part of both thecurrently co-pending U.S. patent application Ser. No. 09/882,708, havinga filing date of 15 Jun. 2001, and of PCT Application No. US01/029504,having a filing date of 20 Sep. 2001, and now issued as Pat. No. WO02/25704 A2 on 28 Mar. 2002; and claims priority from the foregoingapplications, and any parents of the foregoing applications, under theauspices of 35 U.S.C. § 120.

This patent application also incorporates by reference in its entiretyany subject matter previously incorporated by reference into theforegoing-referenced currently co-pending U.S. Patent Applications. Inparticular, this patent application incorporates by reference in theirentireties the subject matter of U.S. Provisional Application No.60/233,996, filed 20 Sep. 2000, and entitled, “Substrate-Level DC BusDesign to Reduce Module Inductance”; U.S. Provisional Application No.60/233,995, filed 20 Sep. 2000, and entitled, “Leadframe-Based Module DCBus Design to Reduce Module Inductance”; U.S. Provisional ApplicationNo. 60/233,994, filed 20 Sep. 2000, and entitled, “Both-Side SolderablePower Devices to Reduce Electrical Interconnects”; U.S. ProvisionalApplication No. 60/233,993, filed 20 Sep. 2000, and entitled“Leadframe-Based Module DC Bus Design to Reduce Module Inductance”; U.S.Provisional Application No. 60/233,992, filed 20 Sep. 2000, and entitled“Press (Non-Soldered) Contacts for High Current electrical Connectionsin Power Modules”; U.S. patent application Ser. No. 09/957,568, filed 20Sep. 2001, issued as U.S. Pat. No. 6,845,017 on 18 Jan. 2005, andentitled, “Substrate-Level DC Bus Design to Reduce Module Inductance”;U.S. patent application Ser. No. 09/957,047, filed 20 Sep. 2001, issuedas U.S. Pat. No. 6,793,502 on 21 Sep. 2004, and entitled, “Press(Non-Soldered) Contacts for High Current Electrical Connections in PowerModules”; and U.S. patent application Ser. No. 09/957,001, filed 20 Sep.2001, issued as U.S. Pat. No. 6,636,429 on 21 Oct. 2003, and entitled,“EMI Reduction in Power Modules Through the Use of Integrated Capacitorson the Substrate Level,” such subject matter being previouslyincorporated by reference into the currently co-pending U.S. PatentApplications.

Each of the foregoing-referenced applications is hereby incorporated byreference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the field of electronics. More specifically,the invention relates to direct current buses (“DC buses”) used in powermodules.

2. Description of the Related Art

An inverter power module is commonly used to convert direct current(“DC”) to alternating current (“AC”) to power a three-phase motor. Thepower module typically has three pairs of switches on a substrate thatis secured to the module baseplate. Each switching pair has a positiveor “high” side switch and a negative or “low” side switch forcontrolling the flow of electric current. Each switching pair isreferred to herein as a “bridge,” and each half of the switching pair isreferred to as a “half-bridge.” The “high side” of the bridge containsthe positive switches, and the “low side” contains the negativeswitches. By the term “switch” is meant a switching device such as aninsulated gate bipolar transistor (“IGBT”) or Metal Oxide Semiconductor(“MOS”) or Metal Oxide Semiconductor Field Effect Transistor (“MOSFET”).

Elements may be described herein as “positive” or “negative.” An elementdescribed as “positive” is shaped and positioned to be at a higherrelative voltage than elements described as “negative” when the powermodule is connected to a power source. “Positive” elements arepositioned to have an electrical connection that is connectable to thepositive terminal of a power source, while “negative” elements arepositioned to have an electrical connection that is connectable to anegative terminal, or ground, of the power source. Generally, “positive”elements are located or connected to the high side of the power moduleand “negative” elements are located or connected to the low side of thepower module.

In a typical power module configuration, the high side switches are onone side of the module opposite the corresponding low side switches. Apositive DC lead from a power source such as a battery is connected to aconducting layer in the high side of the substrate. Likewise, a negativeDC lead from the power source is connected to a conducting layer in thelow side of the substrate. The switches control the flow of current fromthe conducting layers of each half bridge substrate to output leads.Output leads, called “phase terminals” transfer alternating current fromthe three pairs of switches to the motor.

Power modules typically have three bridges combined into a singlethree-phase switching module, or single half-bridge modules that may belinked together to form a three-phase switch. As would be understood byone of ordinary skill in the art, the same DC to AC conversion may beaccomplished using any number of switching pairs, and each switchingpair may contain any number of switches. For simplicity and clarity, allexamples herein use a common three phase/three switching pairconfiguration. However, the invention disclosed herein may be applied toa power module having any number of switches.

Current flows from the positive DC lead to the conducting layer on thehigh side substrate. Current is then permitted to flow through theswitching device on the high side to the conducting layer on the lowside. A phase terminal lead allows current to flow from the conductinglayer on the low side to the motor. The current then flows from themotor to the conducting layer on the low side of a second switching pairto the negative DC lead to the power source.

Current flowing through various paths within the module createsinductances, which in turn results in inductive power losses, reducedefficiency, and the excess generation of heat. When the flow of currentchanges, as in such a high frequency switching environment, largevoltage overshoots often result, further decreasing switchingefficiency. In addition, the DC terminals are commonly attached to oneend of the power module, which forces current to travel further to someswitches, and thus, for some switching configurations, than for others,resulting in non-uniform current loops. Current loops that are notuniform result in uneven or inefficient motor performance.

These and other problems are avoided and numerous advantages areprovided by the device described herein.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a DC bus for use in a power module thatis shaped and positioned to minimize the current loops, thus reducinginductive poser losses. The DC bus is also shaped to permit counter-flowof electric currents, thereby canceling magnetic fields and theirassociated inductances. The DC bus also allows DC current to flowsymmetrically and directly to the switches of the module. Symmetriccurrent loops in the module result in more even and efficient motorperformance.

Elements may be described herein as “adjacent” another element. By theterm “adjacent” is meant that in a relationship so characterized, thecomponents are located proximate to one another, but not necessarily incontact with each other. Normally there will be an absence of othercomponents positioned in between adjacent components, but this is not arequirement. By the term “substantially” is meant that the orientationis as described, with allowances for variations that do not effect thecooperation and relationship of the so described component orcomponents.

In accordance with the present invention, the DC bus for use in a powermodule has a positive DC conductor bus plate and a negative DC conductorbus plate placed parallel to the positive bus. The positive bus isconnected to one or more positive leads, which are connectable to apositive terminal of a power source. The negative bus is connected toone or more negative leads, which are connectable to a negative terminalof a power source. One or more positive connections on the bus arefastenable from the positive bus to the high side of the power modules,and one or more negative connections are fastenable from the negativebus to the low side of the module. The positive bus and the negative buspermit the counter-flow of currents, thereby canceling magnetic fieldsand their associated inductances, and the positive and negative bus areconnectable the power module between the high and low side of themodule. Preferably, the DC bus has separate negative leads and separatepositive leads for each half-bridge on the module. The DC bus may alsoinclude an insulating layer between the positive and negative bus.Preferably, each positive lead is substantially adjacent to a negativelead. The bus may be connected either substantially perpendicular to orsubstantially parallel to the substrate of the power module.

In another aspect of the invention, a power module for reducinginductance is disclosed. The module has a lead frame for supporting themodule and for providing interconnections to the motor and the powersource. A substrate is connected to the lead frame. There are one ormore pairs of high and low switches at the substrate level of themodule. The DC bus described above is placed in the center portion ofthe power module.

In yet another aspect, the invention is directed to a method of reducinginductance in a power module. The method involves allowing DC current toflow symmetrically and directly to the switches of the module andpermitting counter-flow of electric currents, thereby canceling magneticfields and their associated inductances. The positive and negative leadsare positioned in close proximity to one another thereby canceling themagnetic fields and associated inductances.

The DC bus and power module disclosed herein provide improved efficiencyand more even motor performance through the cancellation of magneticfields and minimization of current loops. A parallel negative andpositive DC bus provides the added benefit of creating capacitancebetween the plates, which further minimize voltage overshoots producedby the switching process. These and other advantages will becomeapparent to those of ordinary skill in the art with reference to thedetailed description and drawings.

The foregoing is a summary and thus contains, by necessity,simplifications, generalizations and omissions of detail; consequently,those skilled in the art will appreciate that the summary isillustrative only and is NOT intended to be in any way limiting. Otheraspects, inventive features, and advantages of the devices and/orprocesses described herein, as defined solely by the claims, will becomeapparent in the non-limiting detailed description set forth herein

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is an overhead view of the top of the power module.

FIG. 2 is a perspective view of the power module.

FIG. 3 is a perspective view of the power module without its top portionand with the substrate exposed.

FIG. 4 is the side view of the power module.

FIG. 5 is a cross-sectional front view of the power module with coolingintake and outlet.

FIG. 6 is a cross-sectional front view of the power module withoutcooling intake and out take.

FIG. 7 is a cross-sectional side view of the power module with DCbusleads.

FIG. 8 is a cross-sectional side view of the power module with DC busleads and phase terminals.

FIG. 9 is a top overhead view of the devices on the substrate in themodule.

FIG. 10 is a top overhead view of the printed circuit board in themodule.

FIG. 11 is a perspective view of the power module and DC bus with theprinted circuit board removed.

FIG. 12 is a perspective view of the DC bus.

FIG. 13 is a cross-sectional view of the DC bus.

FIG. 14 is a schematic drawing of a power system according to oneembodiment, including a power module electrically coupled between apower source or power supply, and a load.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the invention, a DC bus is used in a power module,and the DC bus is shaped and positioned to minimize current loops,voltage overshoots and their associated inductance losses, to providefor symmetric current flow. Reference is made herein to a power modulewith three phase terminals for use with a three-phase motor and havingthree bridges, each with two switching pairs. As will be appreciated byone of ordinary skill in the art, the disclosed power module, DC bus,and method for reducing inductance in a power module could be used on apower module with any number of phase terminals and bridges, and havingany number of switching pairs. Nonetheless, for ease of description,reference is made to a three-phase power module.

Referring to FIG. 1, an overhead view of the top of the power module isshown. The module has three positive leads 21 that are connectable to apower source 202 (FIG. 14), such as a battery, and three negative leads23 that are likewise connectable to the negative terminal of a powersource 202 such as a battery, or ground. The module has three sets ofphase terminals 15, 17, and 19.

The top of the power module is held in place by fasteners (not shown)through bushings 13. The fasteners are bolts, but other types offasteners can be substituted therefore, as will be readily apparent tothose of ordinary skill in the art. A non-conducting strip 25 holdsleads 21 and 23 in place by providing a raised portion into which theleads 21 and 23 may be bolted.

As will be understood by one of ordinary skill in the art, the positiveleads 21 and negative leads 23 carry direct current from a batterysource to the module. As will be better understood by the followingdiscussion, the power module converts the direct current to alternatingcurrent. In a three-phase module such as that shown in FIG. 1, there areat lease three phase terminals 15, 17 and 19 through which the resultingalternating current flows. In the preferred embodiment, there are threesets of two phase terminals 15, 17, and 19.

FIG. 2 is a perspective view of the power module 29. The module has amodule frame 11 and top cover 10, which are preferably composed ofplastic. The bottom portion is the cooling header 27 of the module, intowhich a cooling liquid enters, circulates through, and exits, forcooling the module. Sandwiched between the module frame 11 and thecooling header 27 middle portion is the base plate, which contains theprinted circuit board, substrate, and switching devices, and is notshown in this view. FIG. 2 shows the positive leads 21 and negativeleads 23, and phase terminals 15, 17, and 19. The module frame 11 isbolted to the cooling header 27 with bushings 13.

FIG. 3 is a perspective view of the power module, shown without its topcover portion 10 and with the substrate 107 removed. The DC bus 31 has aseparate positive bus plate and a negative bus plate, as is betterillustrated in FIGS. 5-6, and 9-13. The DC bus 31 is arrangedperpendicular to the substrate 107. As would be understood by one ofordinary skill in the art, the substrate has conducting layers separatedby an insulating layer for carrying and controlling a current flow. Thesubstrate 107 has a high side 101 and a low side 103. The substrate 107includes switches 33, which can be IGBTs, MOS, or MOSFETs, and diodes 35for controlling current flow. The switches 33 are preferably IGBTs. Theswitches 33 and diodes 35 are electrically connected, preferably by wirebonding.

As will be understood by one of ordinary skill in the art, directcurrent flows from a power source 202 such as a battery to the positiveDC leads 21 and to the DC conductor bus plates 31. Current flows to aconducting layer in the high side 101 of the power module. The currentflows through the switches 33 and diodes 35 on the high side 101 througha conducting plate 37. The conducting plate 37 is connected to aconducting layer in the low side 103 of the power module by a connectionlocated through a cut-out passage 39 underneath the bus bar. Currentthen flows from the conducting layer on the low side 103 through one ofthe sets of phase terminals 15, 17, or 19 to a three-phase motor 204(FIG. 14). Current from the motor 204 flows back to another set of phaseterminals 15, 17, or 19, where it flows from the conducting layer on thelow side 103 to the negative lead 23 of the bus bar 31 and back to thepower source 202.

FIG. 3 also shows pairs of phase terminals 15, 17, and 19. Three singlephase terminals may be substituted for phase terminal pairs 15, 17, and19. Alternatively, each phase terminal grouping, shown as pairs 15, 17,and 19, may include more than two phase terminals. Pairs of phaseterminals 15, 17, and 19 are used for ease of connecting to switches 33on the high side 103 of the power module.

Three positive DC leads 21 and three negative DC leads 23 are alsoshown. Each lead 21 and 23 is placed central to a switching pairhalf-bridge corresponding to each of the phase terminals 15, 17, or 19.Although other lead configurations are possible, this placement of DCleads 21 and 23 provides for more uniform current flow as opposed toprevious modules having only a single DC lead.

FIG. 4 is a side view of the power module, with DC leads 21 and 23,phase terminal 15, and module frame 11. The bottom cooling header 27includes an intake for coolant 91 and an outlet for coolant 93.

Referring now to FIG. 5, a cross-sectional front view of the powermodule with cooling intake 91 and outlet 93 is shown. The cooling header27 includes a cavity 95 through which a coolant, such as water, mayflow. The cavity 95 includes thermal conducting projections 111. Thecooling header 27 is fastened to the base plate 61, which supports thehigh side switching assembly 55 and low side switching assembly 53. Thephase terminal 15 is also shown. FIG. 5 illustrates the cross section ofthe DC bus at the point having DC leads 21 and 23. The DC bus has apositive conductor plate 59 arranged parallel to a negative conductorplate 57. An electrically insulating layer 51, preferably made fromplastic or tape, is placed between the positive bus plate 59 and thenegative bus plate 57. Alternatively, enough space may be left betweenthe plates 57 and 59 to provide an insulating layer of air or siliconegel. The electrically insulating layer 51 permits more uniform spacingand closer spacing between the positive and negative buses 57 and 59.

Thus, counter flow of current is permitted, thereby canceling themagnetic fields and their associated inductances. In addition, theparallel bus plates 57 and 59 create capacitance. As will be understoodby one of ordinary skill in the art, a capacitor dampens voltageovershoots that are caused by the switching process. Thus, the DC busplates 57 and 59 create a field cancellation as a result of the counterflow of current, and capacitance damping as a result of alsoestablishing a functional capacitance between them. FIG. 5 shows the DCbus plates 57 and 59 placed perpendicular to the high and low sidesubstrates 53 and 55, however, the DC bus plates 57 and 59 may also beplaced parallel to the substrates 53 and 55 and still achieve counterflow of current and reduced inductances.

In various embodiments at least a portion of the materials, referred toherein, which have not been herein identified, described, and/orunderstood by one having ordinary skill in the art as conductive orsemi-conductive (e.g., the materials used in module frame 11, top cover10, the electrically insulating layer 51, etc.), can provide electricalisolation properties (e.g., dielectric properties such as thosepossessed by some plastics and glass). In one implementation, suchdielectric properties include a dielectric strength of approximately 20kV/mm or greater. In another implementation, such dielectric propertiesinclude a dielectric strength of 26 kV/mm. In another implementation,such dielectric properties include an ability to provide dielectricisolation from at or around 2 kV to at or around 5 kV. In anotherimplementation, at least a portion of the materials, referred to herein,which have not been herein identified, described, and/or understood byone having ordinary skill in the art as conductive or semi-conductive,retain their dielectric properties (such as the foregoing-describeddielectric properties) subsequent to undergoing an injection moldingprocess; for example, undergoing injection molding at or around atemperature of 330 degrees centigrade and at or around a pressure of 50mega-Pascals.

In various embodiments at least a portion of the materials, referred toherein, which have not been herein identified, described, and/orunderstood by one having ordinary skill in the art as conductive orsemi-conductive (e.g., the materials used in various implementations ofthe electrically insulating layer 51, etc.), have varying thicknesses.In one implementation, where the materials are to provide electricalisolation between conducting materials (e.g., the electricallyinsulating layer 51 between positive bus plate 59 and the negative busplate 57), the thickness of the materials is a design choice dependentupon a tradeoff between electrical advantage (e.g., generally, providedthe materials can still perform the desired electrical isolation,thinner materials are preferable) and mechanical advantage (e.g., if thematerials are too thin they may be mechanically unstable, and hence mayfracture under normal operation). In one implementation, the thicknessof the materials ranges from 0.1 mm to 1.0 mm. In anotherimplementation, the thickness of the materials is 0.3 mm.

In one implementation, at least a portion of the materials, referred toherein, which have not been herein identified, described, and/orunderstood by one having ordinary skill in the art as conductive orsemi-conductive, can be composites of materials, such as composites ofplastics and glass. For example, in one implementation the module frame11, the top cover 10, and the electrically insulating layer 51, whichhave previously been described as composed of plastic, are insteadimplemented as composites of plastic and glass. In one implementation,the electrically insulating layer 51 has a lower glass content and ahigher plastic content in order to provide better dielectric isolation,while the module frame 11, and the top cover 10, have a higher glasscontent and a lower plastic content to provide better mechanicalstability. Those having ordinary skill in the art will appreciate thatglass provides both mechanical strength and dimensional stability (e.g.,glass generally doesn't immoderately expand or contract withtemperature).

In one implementation, at least a portion of the materials, referred toherein, which have not been herein identified, described, and/orunderstood by one having ordinary skill in the art as conductive orsemi-conductive, can be used to form various embodiments of structuresdescribed herein in various ways. For example, in one implementation,the electrically insulating layer 51 is formed separately andmechanically integrated with other components as described herein, whilein another implementation, the electrically insulating layer 51 isformed of a piece with other components as described herein via aninjection molding process (e.g., injection molding module frame 11 andthe electrically insulating layer 51 as one piece).

In various embodiments at least a portion of the materials, referred toherein, which have not been herein identified, described, and/orunderstood by one having ordinary skill in the art as conductive orsemi-conductive have been implemented using any one or more of thefollowing commercially-available materials: the NOMEX material availablefrom the Dupont Company; Advanced Fibers Systems, 7070 Mississauga Road,Mississauga, Ontario L5M 2H3, Canada; the CIRLEX material available fromthe FRALOCK Company, 120 Industrial Road, San Carlos, Calif. 94070; aPolyphthalamide (PPA) material such as AMODEL AF-1133 VO EngineeringResin available from Amoco Polymers, Inc, 4500 McGinnis Ferry Road,Alpharetta, Ga. 30202-3914; the NORYL GTX830 material available from GEPlastics, One Plastics Avenue, Pittsfield, Mass. 01201; and the HeaterSamicanite material available from Isola Composites, 90101 DELLE France.

The cooling system is further illustrated in FIG. 5. Heat produced bythe power module is conducted through the base plate 61 and theconducting projections 111 to the coolant cavities 95. Coolant flowsinto the coolant intake 91, through the cavities 95, and out coolantintake 93, thereby dissipating heat energy from the power module.

Referring now to FIG. 6, a cross-sectional front view of the powermodule without cooling intake and out take is shown.

Turning now to FIG. 7, a cross-sectional side view of the power modulewith DC bus leads is shown. The coolant cavity 95 runs the length of themodule to intake 91. The high side substrate switches 55 are showninside the module 29 with positive DC leads 21.

FIG. 8 is a cross-sectional side view of the power module with negativeDC bus leads 23 and phase terminals 15, 17, and 19.

FIG. 9 is a top overhead view of the switching devices 33 and diodes 35on the substrate of the module. The positive DC bus plate 59 and thenegative DC bus plate 57 are also shown.

Referring now to FIG. 10, a top overhead view of the printed circuitboard in the module is shown. The positive DC bus plate 59 is allowed toextend into a high side slot in the middle of the module, and thenegative DC bus plate 57 is allowed to extend into a low side slot inthe middle of the module. The DC bus plate has openings for a passage 39from the high side 101 to the low side 103. Substrate switches 33 anddiodes 35 are shown on a printed circuit board. As stated in thediscussion accompanying FIG. 3, the current must be able to flow fromthe conducting layer on the high side 101 of the substrate to theconducting layer on the low side 103 of the substrate. The current flowsfrom the conducting layer of the substrate on the high side 101, throughthe switches 33 and diodes 35 to the conducting plate 37. The conductingplate 37 is connected through the passage 39 to a plate 73 on the lowside 103 of the module.

Referring now to FIG. 11 a perspective view of the power module and DCbus with the printed circuit board, substrate, and switches removed isshown. The DC bus 31 has positive leads 21 connected to the positive busplate 57 and negative leads 23 connected to a negative bus plate 59.

FIG. 12 is a perspective view of the DC bus. The DC bus 31 has positiveDC leads 21 connected to a positive plate 59. The positive plate is inparallel with a negative plate 57, which is connected to negative DCleads 23. The plates are optionally separated by a non-conducting layer51. The DC bus 31 has shorter tabs 81 and longer tabs 83 for forming aconnection with the connecting layer of the substrate. Preferably, thetabs 81 and 83 are wire bonded to the conducting layer of the substrate.The DC bus 31 also has openings 85 through which connections may be madefrom the high side of the substrate to the low side of the substrate.

FIG. 13 is a cross-sectional view of the DC bus 31. A non-conductinglayer 51 separates the negative bus plate 57 from the positive bus plate59. Positive DC lead 21 and negative DC lead 23 are also shown.

FIG. 14 is a schematic drawing of a power system 200 according to oneillustrated embodiment. The power system 200 includes a power module 29electrically coupled between a power supply or power source 202, forexample, a DC power source such as a battery, ultra-capacitor or fuelcell, and an AC load, for example, an electric machine such as anelectric motor 204, for example, a three-phase AC electric motor.

The figures disclosed herein are merely exemplary of the invention, andthe invention may be embodied in various and alternative forms. Thefigures are not necessarily to scale. Some features may be exaggeratedor minimized to show details of particular components. Therefore,specific structural and functional details disclosed herein are not tobe interpreted as limiting, but merely as a basis for the claims and asa representative basis for teaching one skilled in the art to variouslyemploy the present invention.

The foregoing described embodiments depict different componentscontained within, or connected with, different other components. It isto be understood that such depicted architectures are merely exemplary,and that in fact many other architectures can be implemented whichachieve the same functionality. In a conceptual sense, any arrangementof components to achieve the same functionality is effectively“associated” such that the desired functionality is achieved. Hence, anytwo components herein combined to achieve a particular functionality canbe seen as “associated with” each other such that the desiredfunctionality is achieved, irrespective of architectures or intermedialcomponents. Likewise, any two components so associated can also beviewed as being “operably connected”, or “operably coupled”, to eachother to achieve the desired functionality.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art that,based upon the teachings herein, changes and modifications may be madewithout departing from this invention and its broader aspects and,therefore, the appended claims are to encompass within their scope allsuch changes and modifications as are within the true spirit and scopeof this invention. Furthermore, it is to be understood that theinvention is solely defined by the appended claims. It will beunderstood by those within the art that, in general, terms used herein,and especially in the appended claims (e.g., bodies of the appendedclaims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, as an aid tounderstanding, the following appended claims may contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimrecitations. However, the use of such phrases should not be construed toimply that the introduction of a claim recitation by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim recitation to inventions containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should typically be interpreted to mean “atleast one” or “one or more”); the same holds true for the use ofdefinite articles used to introduce claim recitations. In addition, evenif a specific number of an introduced claim recitation is explicitlyrecited, those skilled in the art will recognize that such recitationshould typically be interpreted to mean at least the recited number(e.g., the bare recitation of “two recitations,” without othermodifiers, typically means at least two recitations, or two or morerecitations).

Having thus described the invention, the same will become betterunderstood from the appended claims in which it is set forth in anon-limiting manner.

1. A method of reducing inductance in a power module comprising: allowing DC current to flow symmetrically and directly to the switches of the module; permitting counter-flow of electric currents, thereby canceling magnetic fields and their associated inductances; and simultaneously positioning the positive and negative leads in close proximity to one another thereby canceling the magnetic fields and their associated inductance.
 2. The method of claim 1, further comprising: mounting a DC positive bus plate and a DC negative bus plate parallel to one another between the high and the low side of the power module.
 3. The method of claim 1, further comprising: placing an insulating layer between the positive bus and the negative bus.
 4. The method of claim 1, further comprising: providing separate power leads to each half-bridge of the power module.
 5. The method of claim 1 wherein said step of allowing DC current to flow symmetrically and directly to the switches of the module comprises: allowing current to flow from a negative terminal of a power source directly to said switches without being redirected through any additional components, and allowing current to flow from a positive terminal of a power source directly to said switches without being redirected through any additional components.
 6. The method of claim 5 wherein said step of allowing DC current to flow symmetrically and directly to the switches of the module comprises allowing current from a negative terminal of a power source, and current from a positive terminal of a power source to flow symmetrically to said switches.
 7. The method of claim 1 wherein said step of allowing DC current to flow symmetrically and directly to the switches of the module comprises allowing current from a negative terminal of a power source, and current from a positive terminal of a power source to flow symmetrically to said switches.
 8. The method of claim 1 wherein a first circuit within said module directly connected to a positive lead of said module and a second circuit within said module directly connected to a negative lead of said module are symmetrical.
 9. The method of claim 8 wherein said first and second circuits are symmetrical about an axis defined by adjacent edges of said first and second circuit. 